The Burren is a 135 square mile limestone plateau in County Clare, Ireland. It's a fascinating place to see and experience. The limestone was formed millions of years ago under a tropical sea and then it was shaped by hard weather and ice. Walking on it is tough as you are constantly looking down trying not to fall in the cracks. One of the places on The Burren that is highly recommended for a visit is the portal dolmen at Poulnabrone (photographed above). A dolmen is a megalithic tomb formed out of stone that looks like a table.